1. Field of the Invention
The present invention relates to a playback apparatus suitable for reproducing address data from a disk record medium, in particular, from a recordable optical disk.
2. Description of the Prior Art
Some optical disks having wobbled grooves are known. The grooves are wobbled with a particular signal, for example, a carrier signal of 22.05 KHz. They are used to perform CLV control. Moreover, a particular optical disk where the carrier signal is frequency-modulated with absolute time data, which is so-called ATIP (Absolute Time In Pre-groove) so as to form the above mentioned grooves in accordance with the FM signal, has been proposed. In this optical disk, absolute time data from the start track to the last track which is represented with ATIP is used as address information. By accurately reading ATIP, a particular position can be located on a recordable optical disk. ATIP is included in a push-pull signal which is formed with reflected light from the optical disk and ATIP is read by decoding the push-pull signal.
When a signal obtained from an optical disk through a pickup is detected and reproduced, if a push-pull signal is formed in accordance with reflected light of a pit portion, a signal component being recorded leaks in the push-pull signal. Thus, the C/N of the push-pull signal deteriorates and thereby getting into difficulty for reproducing ATIP.
For example, in the case of a CD-WO on which an EFM signal is recorded, the spectrum of the ATIP signal is centered at a frequency of 22.05 KHz.+-.1 KHz. On the other hand, the EFM signal being reproduced is a pulse train with a frequency ranging from 200 to 720 KHz. The low band component of the EFM signal is also present in the band of the ATIP signal, thereby deteriorating the C/N.
In addition, as described earlier, since a particular position is located on the recordable optical disk in accordance with ATIP, when it is difficult to reproduce ATIP, a particular position cannot be located. Consequently, data cannot be recorded on the recordable optical disk. In addition, designated data cannot be recorded additionally in a designated position. Thus far, the measures against this problem has been required.